Thermostatic control device

ABSTRACT

A transmission thermostat adapted to control the flow of automatic transmission fluid between a transmission and a transmission oil cooler including a temperature-sensitive mechanism. The temperature-sensitive mechanism includes at lease one bimetallic coil.

FIELD

The present invention generally relates to a thermostat and moreparticularly, to a vehicular thermostat for transmission oil. Thepresent invention employs a bimetal element to cause opening and closingthe flow of oil through a heat exchanger rather than a wax motor.

BACKGROUND

The automatic transmission of a motor vehicle requires cooling, which isachieved by flowing the automatic transmission fluid (ATF) through atransmission oil cooler. However, it is desirable to be able to controlthe flow of oil through said cooler, because cooling the ATF when it iscold enough can be detrimental, causing the oil to become too viscousfor the proper operation of the transmission. It is desirable to allowthe ATF to flow through the cooler only when cooling is actuallyrequired. At all other times the ATF should be recycled back to thetransmission without flowing through the oil cooler. The presentinvention provides a reliable and cost-effective method to automaticallybypass the ATF back to the transmission when the ATF does not requirecooling.

SUMMARY

Efforts have been made in the past to use a wax element to control theflow of ATF. However, this approach has reliability issues, because thehigh temperature and the high pressure under which an oil thermostatoperates make it prone to failure. Even in more traditional uses, suchas in water thermostats for engines, which typically operate a lowertemperatures and lower pressures than the transmission, the waxthermostat is a failure-prone component because of the tendency of thewax to leak out of the wax capsule. In an oil application the use of awax motor is even riskier.

It is an object of present invention to provide a thermostat thateliminates the wax element failure mode.

It is another object of present invention to provide a thermostat thatis rugged and more reliable than conventional transmission thermostats.

It is still yet another object of present invention to provide atransmission oil thermostat with all the above benefits.

According to one particular aspect, the present teachings provide atransmission thermostat for controlling the flow of automatictransmission fluid between a transmission and a transmission oil cooler.The thermostat includes a temperature-sensitive mechanism. Thetemperature-sensitive mechanism may include at least one bimetalliccoil.

DRAWINGS

FIG. 1 is a view of a thermostatic control device constructed inaccordance with the present teachings.

FIG. 2 is a view of another thermostatic control device constructed inaccordance with the present teachings, the thermostatic control deviceincluding a pressure-relief valve.

FIG. 3 is a side view of the thermostatic control device of FIG. 2.

FIG. 4 is a cross-sectional view of the thermostatic control device ofFIG. 2.

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

FIG. 1 shows a preferred embodiment of the invention. The transmissionoil thermostat of FIG. 1 regulates the oil flow between an automatictransmission (TRANS) and the transmission oil cooler (TOC). Oil flowsfrom the automatic transmission to the thermostatic valve, then,depending on the temperature of the incoming oil, the valve eitherdirects the oil to flow to the transmission oil cooler or directly backto the transmission.

At the heart of the device of FIG. 1 is a bi-metallic element thatreacts to temperature changes of the incoming oil by opening and closingports. In this embodiment the bimetal element is shaped like a coil.Bimetal coils experience a certain degree of winding or unwinding whensubjected to a change in temperature. In other words, there is arelative rotation between the ends of the bimetal coil when thetemperature changes. The angle of rotation is proportional to thetemperature change and it is very consistent and repeatable. The rotarymovement of the bimetal coil is used to open or close the ports of thedevice. Under cold conditions, the bimetal element senses thetemperature of the incoming oil that it is exposed to and closes theports that communicate with the transmission oil cooler while openingthe by-pass ports that directly channel the cold oil back to thetransmission. Under hot conditions, the bi-metal element opens the portsthat allow flow to the transmission oil cooler while it closes theby-pass ports.

The bi-metallic oil thermostat is a device that controls and directs theflow of oil from the transmission to either the transmission oil cooler,or back to the transmission when no cooling is required.

FIG. 1 shows a preferred embodiment of the invention. The transmissionoil enters the housing (1) through port (2). The oil flows over thebimetal coil (3) communicating its temperature to it. The bimetal coilis connected to shaft (4), which is connected to rocker arms 31 and 32.Sealing plates 7, 8, 9 and 10 are attached to the ends of the rockerarms. The mission of the sealing plates is to open or close the orifices21, 22, 23 and 24 on the capsule (6) in order to control and route theoil flow.

Under a cold oil condition, the bimetal coil (3) rotates the shaft (4),causing plates (7) and (8) to open and plates (9) and (10) to close.When plates (7) and (8) are open, the oil flows back to the transmission(TRANS) through port (11) with minimal impedance. Therefore thethermostat is in by-pass mode, preventing the oil to reach thetransmission oil cooler (TOC).

As the oil temperature rises and the hot oil condition is reached, thebimetal coil (3) rotates the shaft (4) closing plates (7) and (8) whilesimultaneously opening plates (9) and (10). When orifices (21) and (22)are open, the oil communicates with port (12); thus flowing toward thetransmission oil cooler (TOC). Oil then circulates through the heatexchanger, and returns to the housing (1) through port (13), thencontinues through port (11) with minimal impedance back to the pumpingsource.

When orifices (23) and (24) are closed in a hot condition, no oil isbypassing the cooler circuit. When orifices (21) and (22) are closed ina cold condition, no oil is allowed to flow through the cooler circuit.In thermal transition, all plates (7),(8), (9) and (10) are partiallyopen allowing a modulated portion of oil to flow to the cooler circuitvia port (12) and a portion to be bypassed through port (11).

FIG. 2 shows a similar embodiment of the invention which alsoincorporates a pressure relief valve. Under excessive high pressuresituations, which can happen when the oil is cold and takes on agel-like consistency, a pressure relief valve (64) will open allowingoil to bypass the cooler circuit and flow to port (11) via relieforifice (65).

FIG. 3 shows a side view of the transmission oil thermostat.

FIG. 4 shows a cross-section of the thermostat with the closed sealingplates 41 and 42 and the open sealing plates 43 and 44. A change in thetemperature of the oil can cause a rotation of the bimetal coil 45,causing a reversal of the status of the plates. The plates are clockedthrough the connecting shaft (not shown in FIG. 4) so that either 41 and42 are open and 43 and 44 closed, or vice versa.

The plates are designed in a balanced way, so that for instance when theoil pressure tries to close plate 41, it simultaneously tries to openplate 42, creating a zero net torque on the connecting shaft. Thebalanced design is key to this thermostat, because it allows the bimetalcoil to control the rotation of the shaft with the relatively smalltorque exerted by the coil, which would be insufficient to overcome thehigh oil pressure forces if such a balanced approach was not used. Thebalanced design cancels the forces created by the oil pressure, allowingthe bimetal coil to rule.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.The same may also be varied in many ways. Such variations are not to beregarded as a departure from the disclosure, and all such modificationsare intended to be included within the scope of the disclosure.

1. A transmission thermostat adapted to control the flow of automatictransmission fluid between a transmission and a transmission oil coolerby using a temperature-sensitive mechanism that comprises at least onebimetallic coil.
 2. The transmission thermostat of claim 1, wherein theat least one bimetallic coil actuates a plurality of sealing elementsthat route the oil in a temperature dependent pattern.
 3. Thetransmission thermostat of claim 1, wherein the sealing elements arearranged in a balanced way such that the force created by the oilpressure acting on one sealing element is canceled out by anothersealing element, generating a substantially zero net torque that allowsthe at least bimetallic coil to rule.
 4. The transmission thermostat ofclaim 1, consisting of a housing with a pressurized fluid input port, afluid output port leading to a fluid cooling device, a return port forthe fluid coming back from the fluid cooling device and a return portleading the fluid back to its pressure source.
 5. The thermostat ofclaim 4, wherein where the thermostat contains an internal pressurerelief mechanism, such as but not limited to a spring-loaded element, aleaf spring or other flexible element covering an orifice.